1. Field of the Invention
The invention relates to an eye-type buttonhole sewing machine.
2. Background Art
U.S. Pat. No. 6,095,066 describes an eye-type buttonhole sewing machine with a needle drivable in up and down reciprocation. It comprises an x-y table which is displaceable by stationary stepper motors mounted on the sewing machine. The x-y table is supported by way of vertical, parallel rods so that displacement in the x direction is arched. Actuation in the x direction is effected via a toothed quadrant that is coupled with a shaft with an oscillating lever mounted thereon. Actuation in the y direction takes place via an electric motor by means of a threaded spindle which runs in the y direction and the spindle nut of which is joined to the y carriage by a sliding coupling. Drawbacks reside in that accurate working of the stitch-forming tools i.e., of the needle, hook etc., is restricted or, for greater displacements, not at all attainable due to the fact that the guidance of the table is acceptable only with some reservations. Further drawbacks reside in that a considerable number of components is required, having a corresponding mass, which demands for strong dimensioning of the stepper motors.
Prior public use by Applicant has disclosed an eye-type buttonhole sewing machine in which an x-y table of the above design is drivable in the y direction by a belt drive. The oscillating levers which perform the motion in the x direction are drivable by a cam drive. The design has the additional drawback that the belt drive possesses a certain elasticity, allowing accurate positioning only to a certain extent.
It is an object of the invention to embody an eye-type buttonhole sewing machine in which motion in the x and y direction may take place very easily and accurately.
According to the invention, this object is attained in an eye-type buttonhole sewing machine, comprising a needle which is drivable in up and down reciprocation; an x-y table which supports an x carriage mounted on the sewing machine for displacement only in an x direction, and a y carriage mounted on the x carriage for displacement only in a y direction; an x motor in the form of an electric motor mounted on the sewing machine, which x motor is directly coupled with the x carriage via a drive that translates a rotary motion into a linear motion; and a y motor in the form of an electric motor mounted on the sewing machine, which y motor is directly connected to the y carriage via a threaded spindle and a spindle nut and a sliding coupling which extends in the x direction. The design according to the invention helps accomplish that the x-y table, with a work piece resting thereon, is guided precisely on an x-y level, not performing any vertical motion perpendicular thereto. With the drive which converts the rotary motion into a linear motion acting directly on the x carriage, components are saved and actuation virtually free from play is rendered possible. Likewise, the y drive is free from play because of direct conversion. Since the drives act directly on the respective x and y carriage in the x and y direction, also the mass of conversion elements is low so that strong acceleration and high positioning accuracy are attained, accompanied with driving motors of correspondingly restricted design.
Details of the invention will become apparent from the ensuing description of an exemplary embodiment, taken in conjunction with the drawing.